Periodically hydrologic alterations decouple the relationships between physicochemical variables and chlorophyll-a in a dam-induced urban lake

摘要

Periodically hydrologic alterations driven by seasonal change and water storage capacity management strongly modify physicochemical properties and chlorophyll-a(Chl-a)and their interactions in dam-induced lakes.However,the extent and magnitude of these changes still remain unclear.This study aimed to determine the effects of periodically hydrologic alterations on physicochemical variables and Chl-a in the dam-induced urban Hanfeng Lake,upstream of Three Gorges Reservoir.Shifts in Chl-a and 13 physicochemical variables were recorded monthly in the lake from January 2013 to December 2014.Chl-a was neither seasonal nor inter-annual differences while a few physical variables such as flow velocity(V)exhibited significantly seasonal variabilities,and chemical variables like total nitrogen(TN),nitrate-nitrogen(NO3-N),total phosphorus(TP),dissolved silica(DSi)were markedly inter-annual differences.Higher TN:TP(40:1)and lower NO3-N:DSi(0.8:1)relative to balanced stoichiometric ratios suggested changes in composition of phytoplankton communities and potentially increased proportion of diatom in Hanfeng Lake.Chl-a was predicable by combination of dissolved oxygen(DO),TN and DSi in dry season,and by V alone in wet season.During the whole study period,Chl-a was solely negatively correlated with TN:TP,indicating decline in N concentration and increase in P could therefore increase Chl-a.Our results highlight pronounced decoupling of linkages between Chl-a and physicochemical variables affected by periodically hydrologic alterations in dam-induced aquatic systems.